Free edge-sealed film articles

ABSTRACT

Free edge-sealed film articles and a method for making such, wherein the articles comprise a plurality of film portions and contain a free edge-seal between two of such portions, with one or both of the two free edge-sealed portions consisting essentially of a plurality of layers of diverse thermoplastic materials which are so ordered that on sealing the two portions together, the layered film portion is curled toward the other of the two free edge-sealed portions.

CROSS REFERENCE TO RELATED APPLICATION

This is a divisional application of allowed application Ser. No.07/994,605, filed Dec. 21, 1992 now U.S. Pat. No. 5,292,392. ApplicationSer. No. 07/994,605 is a continuation of abandoned application Ser. No.07/513,537, filed Apr. 23, 1990.

FIELD OF THE INVENTION

The present invention relates to that class of film articles which willfor present purposes be termed the "free edge-sealed" film articles andto methods for making such articles, and more particularly, to sucharticles comprising film portions which consist essentially of aplurality of layers of diverse thermoplastic materials.

Many film articles are currently made by processes involving theapplication of heat, solvents or the like to adjacent film portions toeffect a seal therebetween, wherein at the point of application or atthe location where a seal is effected, the adjacent film portions arefundamentally unsupported and thus possess some freedom of movement torespond to the application of such heat. Manufacturing processes whichcan be characterized in this fashion are described, for example, in U.S.Pat. Nos. 3,508,378 to Fehr et al., 3,736,219 to McTaggart, 3,947,198 toHutt, 4,055,452 to Carlisle, and 4,502,906 to Young et al. Each of theseprocesses involve the application of some film-sealing medium or meansacross a gap between two film plies, wherein the film plies are notpinched or pressed between a pair of heated surfaces in sealing theplies together but in a sense are sealed between two "free" edges orportions of the plies.

The "free edge-sealed" articles to which the present invention relateswill, then, be understood to encompass the broad spectrum of filmarticles made by the processes characterized according to the precedingparagraph.

Among the many film articles which may be described as "freeedge-sealed" are the majority of reclosable plastic storage bags. In thecontext of such reclosable plastic storage bags, it has been appreciatedthat bags having sides, bottoms and constituent film portions generallywhich consist essentially of a plurality of layers of diversethermoplastic materials can have better structural and/or barrierproperties than bags made from a blend of such materials or from asingle material only. These improved properties, for example, improvedpuncture and/or barrier resistance, are highly desirable in theconsumer's eyes.

In previous constructions of free edge-sealed film articles such asthese reclosable plastic bags wherein diverse thermoplastic materialshave been used, the materials have been used in a single blend layer orin a layer structure within a layered film portion which is balanced interms of the moduli of the layers in the structure. These articles havebeen constructed in the manner indicated at least in part because ofconcerns over the curling at room temperature of plural layer films ofthe various diverse materials.

Each of the film portions in the single blend layer and balanced layerconstructions handles and seals essentially in the fashion of a layer ofa single material, with the seal strength of a seal between adjacentfilm portions being dependent generally on the same factors known to beimplicated in determining the seal strength of free edge-sealed filmportions comprised of a single material. These factors include whetherthe film portions to be joined are properly clamped, the gauge of thefilm portions to be joined, and the tension placed on the film portions.

Manufacturers of free edge-sealed film articles have because of thesefactors experienced significant difficulties in the past in achievingconsistent seals, and these poor or inconsistent seals can limit theimprovement in barrier or structural properties which can be achieved bythe use of diverse and perhaps more costly materials, in addition toreducing the appeal of the articles to consumers.

It would be desirable, then, if free edge-sealed articles could be madewherein an improvement in properties realized by a combination ofdiverse materials in the articles and the consumer appeal of such acombination were not limited or even overcome by the formation of weakor incomplete seals between film portions in a significant number of thearticles.

SUMMARY OF THE INVENTION

The present invention fulfills this desire by providing a freeedge-sealed film article which is comprised in general terms of aplurality of film portions and which contains a free edge-seal betweentwo of the plurality of film portions. At least one of the two freeedge-sealed film portions consists essentially of a plurality of layersof diverse thermoplastic materials and is curled toward the other of thetwo film portions along at least a portion of the free-edge seal infree-edge sealing the film portions together.

Thus, it may be that only one of a respective pair of free edge-sealedfilm portions is layered, with the other film portion being comprised ofa single layer only and only the one layered film portion curling towardthe single layer portion on sealing the two portions together. Or, bothof the two free edge-sealed film portions may be layered, but with oneof the two film portions having a balanced structure such that againonly one of the two layered film portions is curled toward the other.Or, both of the two film portions may be layered, and the layers withineach ordered so that on sealing the two film portions together both filmportions are curled toward the other.

The curling of a given film portion toward a second film portion duringthe free edge-sealing of such film portions enables the formation of asuperior seal between the two film portions on a more consistent basis,as particularly evidenced by a lesser likelihood of leaks in certainreclosable plastic containers constructed in accordance with the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary cross-sectional view of apparatus for freeedge-sealing two layered film portions together.

FIG. 2, taken along line 2--2 of FIG. 1, is an enlarged fragmentarycross-sectional view of the two layered film portions to be freeedge-sealed together.

FIG. 3 is an enlarged fragmentary cross-sectional view of a typical beadformed by a single layer film portion of substantially uniformcomposition on contact with a hot sealing wire in one free edge sealingmethod.

FIG. 4 is an enlarged fragmentary cross-sectional view of a typical hotwire, free edge seal between two single layer film portions of the typeshown in FIG. 3.

FIG. 5 is an enlarged fragmentary cross-sectional view of the formationof the seal between two layered film portions constructed and stacked asin FIGS. 1 and 2, and sealed in the same fashion as the stacked singlelayer film portions in FIG. 4.

FIG. 6 is an enlarged fragmentary cross-sectional view of a completedfree-edge seal between the two layered film portions in FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, and more particularly to FIG. 6, apreferred construction of the free edge-sealed film articles of thepresent invention is depicted and denoted by the numeral 10. In thispreferred construction, the film article is comprised of a plurality offilm portions, with two of these film portions being the film portions12 and 14 variously shown in FIGS. 1, 2, 5 and 6.

Referring now to FIG. 1, the film portions 12 and 14 are shown beingclamped by opposing elements 11 and 13 in position to be sealed togetherin a free edge-sealing apparatus 15, the free edge seal to be formedapproximately along the line 2--2 by free edge sealing means such as ahot wire 16. As has been previously noted and as is well known in theart, a gap 17 is often formed between the film portions 12 and 14 in aclamped condition which must be bridged in order to obtain an effectiveseal between the film portions 12 and 14. This gap 17 and the preferredconstruction of the layered film portions 12 and 14 are evident in FIG.2.

In the preferred construction of the film portions 12 and 14 shown inFIG. 2 the film portions 12 and 14 are substantially identicallyconstructed of layers 18 and 20 of two diverse thermoplastic materials.The "diverse thermoplastic materials" are defined for purposes of thepresent invention as those materials which are characterized bydiffering amounts of frozen-in stress or differing melt propertiesgenerally, whereby on melting in the presence of the hot wire 16 thelayers 18 and 20 retract at faster and slower rates, respectively, fromthe hot wire 16.

The "frozen-in stress" mentioned above can be considered a residuallevel of stress contained in layers 18 and 20, primarily as a functionof the character of the materials comprising those layers. For example,the extrusion and drawing down in a conventional film manufacturingprocess of low density polyethylene(LDPE) can be seen to produce a levelof residual or frozen-in stress in the resulting film layer due to thelong side chains (comprising fifty or more carbon atoms) in the LDPEbeing bent and stretched alongside the backbone of the LDPE molecules.By the same token, the extrusion of linear low densitypolyethylene(LLDPE) (with side chains of fifteen and fewer carbons,generally) can be seen to result in comparatively lower amounts offrozen-in stress in the resulting film layer.

The stresses involved are "frozen-in" in the sense that the materials inlayers 18 and 20 are at least temporarily fixed in a different spatialconfiguration than the lowest potential energy configuration to whichthey would naturally be inclined in a molten state.

With a proper selection of materials and of a thickness for each of thelayers 18 and 20 formed from these materials, it can be seen that thediffering rates of retraction experienced by layers 18 and 20 on freeedge sealing can create a net bending moment in film portions 12 and 14,so that the ends of the film portions 12 and 14 are curled toward oneanother in forming a seal in the manner shown in FIGS. 5 and 6 anddescribed below. This tendency to curl toward one another on sealing, itwill be appreciated, will be advantageous in bridging the gaps 17 whichmight be formed between layered film portions 12 and 14 when clampedtogether in the sort of free edge sealing apparatus 15 depicted in FIG.1.

A free edge-sealed reclosable plastic storage bag having substantiallyidentically constructed film portions 12 and 14 consisting essentiallyof a low density polyethylene layer 18 and a linear low densitypolyethylene layer 20, for example, demonstrates a tendency for the twofilm portions 12 and 14 to curl together where the linear low densitypolyethylene selected has a density of from about 0.912 to about 0.941grams per cubic centimeter and where the linear low density polyethylenelayer 20 comprises on the average about 30 to about 70 percent of thethickness of film portions 12 and 14.

In contrast is the behavior of film portions 12a and 14a which areconstructed from a homogeneous blend of materials, from a singlematerial, or as a balanced set of layers of diverse materials whensealed in the manner suggested by FIG. 1. As can be seen from FIGS. 3and 4, film portions 12a and 14a retract from a wire 16 uniformly andwithout curling, while showing however a slight inclination in thedirection of movement of the wire 16.

The free-edge seal between such portions 12a and 14a results from theportions 12a and 14a being clamped closely enough, given the size of thebeads formed in portions 12a and 14a for the beads to run into oneanother or abut. Thus, the formation of an acceptable seal between filmportions 12a and 14a which are comprised of a blend of materials, asingle material, or a balanced set of layers of various materials isdependent as mentioned previously on such factors as whether the filmportions to be joined are properly clamped, the gauge of the filmportions to be joined, and the tension placed on the film portions.

On the other hand, as may be seen with particular reference to FIG. 5,when the layered film portions are properly constructed and arranged inaccordance with the present invention, the beads formed by the layeredfilm portions are predisposed to form a seal with a respective filmportion by expanding or curling in the direction of arrows 22 towardthat film portion during the free-edge sealing process.

As has been suggested previously, while a preferred embodiment of thefree edge-sealed articles of the present invention is as describedabove, a number of other embodiments are possible and may be employed ifdesired. For example, the film portions 12 and 14 can individuallycontain or can each contain any number of layers of any number ofdiverse thermoplastic materials, so long as on sealing the two filmportions 12 and 14 together the cumulative effect of the layers withinat least one of the two film portions 12 and 14 is the curling towardthe other of the two film portions 12 and 14 along at least a portion ofthe free-edge seal formed between film portions 12 and 14.

It will also be appreciated that a free edge-sealed film articleconstructed in accordance with the teachings of the present inventionmay be comprised of a number also of other layered film portions to befree edge-sealed to a single layer film portion, or to a differentlayered film portion of the same or a different construction.

It may be desirable for still other applications to create a localizedzone of weakness in the seal between two film portions, at least one ofwhich is layered in such a fashion that on free edge-sealing the twofilm portions together the layered film portion is curled toward theother film portion along at least a portion of the sealed area. Alocalized zone of weakness in a different portion of the seal can beachieved for example by altering the relative thicknesses of layerswithin a layered film portion so that it curls away from, rather thantoward, the other film portion to which it is being sealed. In anotherembodiment, seals between film portions may be made of differentstrengths, so that for instance a completely sealed plastic filmcontainer is preferentially ruptured along certain seals.

Considering, however, more conventional and presently commerciallysignificant uses of free edge-sealed film articles, it will normally bedesirable to employ the teachings of the present invention to formuniformly stronger seals (in the sense of requiring a greater energy tobreak the seals) between free edge-sealed film portions. For example, amost preferred embodiment of the articles of the present invention willbe as reclosable plastic containers of the type having two flexibleopposed free edge-sealed sidewalls and an interlocking closure mechanismwhich is operable for being interlocked over a predetermined length andwhich is connected to the two sidewalls adjacent an open end of thecontainer.

More particularly, the most preferred reclosable plastic containers ofthe present invention will be characterized by two opposed flexiblesidewalls free edge-sealed along at least two edges, and an interlockingclosure mechanism comprising a pair of opposed interlocking rib- andgroove-type closure members which may be interlocked to substantiallyeffect a sealing closure of the adjacent open end of the container.

The opposed flexible sidewalls are preferably substantially identicallyconstructed with each being from about 1 to about 4 mils in thicknessand consisting essentially of an inner layer 18, relative to theinterior of the bag, of low density polyethylene, and an outer layer 20of a linear low density polyethylene having a density of from about0.917 to about 0.935 grams per cubic centimeter. The outer LLDPE layer,further, should preferably comprise from about 35 to about 65 percent,and most preferably about 45 to about 55 percent of the thickness of arespective sidewall on the average.

The most preferred reclosable plastic containers should preferably haveat least one and most preferably both of the sidewalls curl toward theother sidewall on sealing the same together, such that the reclosableplastic containers so constructed leak to a significantly lesser extentwhen blown up in the manner of a balloon and submersed underwater thanreclosable containers which are substantially identically constructed,blown up and submersed but which comprise sidewalls consistingessentially of the same diverse materials in a substantially homogeneousblend. As a measure of this improved sealing made possible by thepresent invention, the reclosable plastic containers of the presentinvention should preferably have less than about 20 percent of theleaks, and most preferably less than about 10 percent of the leaks seenin the same container but with blended rather than layered sidewalls.

A preferred method of making a free edge-sealed film article such asdescribed herein would involve coextruding layers of diversethermoplastic materials in a continuous film web, while ordering anddimensioning the layers according to differing levels of frozen-instress, for example, to create a tendency to curl in the assembledlayers in a free edge-sealing process. A first portion from the film webcould then in one embodiment be inverted in stacked relationship to asecond, preferably substantially identically constructed portion of thesame or a different film web as shown in FIG. 1, and sealed thereto. Ina most preferred method of making the free edge-sealed film articles ofthe present invention, the layered first and second portions wouldcomprise adjacent portions of the same continuous film web, and theinverting and stacking of the first portion with respect to the secondwould be accomplished simply by folding the film web intermediate thefirst and second portions.

ILLUSTRATIVE EXAMPLES

The following examples are offered to illustrate the present inventiononly, and should not be taken to in any way limit the scope of theinvention as defined by the claims which follow.

EXAMPLES 1

In this example, single layer film portions of an average thickness ofabout 1.7 mils were produced by blending 50 percent by weight of a lowdensity polyethylene and 50 percent by weight of a linear low densitypolyethylene having a density of about 0.935 grams per cubic centimeter,and extruding the substantially homogeneous blend in a conventional castfilm process to a chill roll. These single layer film portions wereobserved microscopically to form a generally triangularly-shaped beadsuch as shown in FIG. 3 when exposed to a hot sealing wire. The slightupward tilt of the bead again typically reflects the direction ofmovement of the hot wire in a hot wire, free edge-sealing apparatusrelative to the film portion. The single layer film portions whenclamped and wire-sealed together on a manually controlled wire sealerproduced a seal having the general appearance of two triangles joinedalong a side, such as shown in FIG. 4.

For comparison, layered film portions having discrete layers 18 and 20formed from the same LDPE and LLDPE, respectively, were made bycoextruding the LDPE and LLDPE layers 18 and 20 to a chill roll in thesame cast film process as employed with the single blend layer. TheLLDPE layer 20 comprised about 50 percent of the thickness of thecoextruded film, on the average.

When the LDPE layer 18 of a given layered film portion was placed in aposition to be exposed to the same hot sealing wire after the LLDPElayer, an upward curving, generally oval-shaped edge bead was formed.Where the LDPE layer 18 was placed in a position to be exposed to thewire first, the edge bead still curved downward, even despite theinherent tendency of an edge bead to curve somewhat in the direction ofmovement of the hot sealing wire generally.

A comparison of the seal shown in FIG. 4 and an enlarged cross-sectionalview (FIG. 6) of the seal between two film portions 12 and 14 withlayers 18 and 20 of LDPE and LLDPE arranged as in FIGS. 1 and 2 suggeststhat the edge beads formed in the layered film portions of the presentinvention cooperatively "knit" together rather than merely abutting oneanother as in the known art. The integrity of the seal in the freeedge-sealed articles of the present invention are as a result believedto be less dependent on such factors as whether the film portions to besealed are properly clamped or not, so that adequate seals should bemore consistently and reliably achieved.

It should be noted that thinner gauge layered film portions were as arule observed to curl even more strongly in a given direction thanthicker gauge films. Whereas thinner gauge films of a conventionalconstruction would form smaller beads, and thus would presumably begiven to greater sensitivity to clamping defects and like difficulties,the comparative benefit provided in terms of sealing by a layered andordered film portion as described herein should be even more pronouncedfor films of an average thickness of about 2.0 mils or less.

EXAMPLE 2

For this example, a number of sets of reclosable plastic storagecontainers of the type having two opposed flexible sidewalls of anaverage thickness of about 2.0 mils, and a pair of opposed rib- andgroove-type closure members were constructed by standard commercialmethods and equipment.

The sidewalls of a container in a particular set were substantiallyidentically constructed to one another, and to sidewalls of the othercontainers in a set, by extruding or coextruding in a cast film processa low density polyethylene and/or a linear low density polyethylenehaving a density of about 0.935 grams per cubic centimeter in variouscombinations. The resulting films were: 100% low density polyethylene(set "A"); a blend of 70% by weight of low density polyethylene and 30%by weight of the LLDPE (set "B") a coextruded film with a LDPE layercomprising 70% of the film thickness and with a LLDPE layer comprisingthe remaining 30% of the film thickness (set"C"); a coextruded filmhaving a LDPE layer and a LLDPE layer which each comprised 50% of thethickness of the coextruded film (set "D"); a coextruded film having aLDPE layer comprising 30% of the film thickness and a LLDPE layercomprising the other 70% of the film thickness on average (set "E") and100% of the LLDPE (set "F").

Rib- and groove-type closure members were conventionally applied to theLDPE side of these films, if any, and the films folded over one anotherfor wire sealing on a manually controlled wire sealer with the LDPElayers facing inwardly. One hundred containers were formed for each setby identically sealing the sidewalls together from the area of the foldcompletely through the closure members, so that the containers couldthereafter be blown up, immersed and tested for leaks along the wireseals in the various sets of containers.

To accentuate any differences between the various sets, several thingswere purposely done which are conventionally known to cause leaks alongthe wire seals of such containers. For example, the closure members wereoriented upside down with respect to the notch placed in the hold-downbar to accommodate the closure members.

The completed containers were then blown up, the closure members wereengaged to seal off the respective open ends of the containers, and thecontainers immersed underwater. The containers for each set wereobserved for signs of leaks along the wire-sealed right and left sidewelds, in the right and left bottom corners, and adjacent the closuremembers at the right and left sides of the containers.

Table 1 reports the number of leaks observed in the hundred containersof each set that were formed and tested, the location of the observedleaks, and the distribution of the leaks among the hundred containerswithin the set.

                  TABLE I                                                         ______________________________________                                                       Set    Set    Set  Set  Set  Set                               Location       A      B      C    D    E    F                                 ______________________________________                                        Left Bottom Corner                                                                           84     76     1    5    0    93                                Right Bottom Corner                                                                          98     99     9    0    0    100                               Sum, Bottom Corners                                                                          182    175    10   5    0    193                               Left Side Weld 18     20     1    3    20   49                                Right Side Weld                                                                              12     10     0    0    44   40                                Sum, Side Welds                                                                              30     30     1    3    64   89                                Left Closure Member                                                                          52     35     0    1    1    50                                Right Closure Member                                                                         79     67     1    2    2    46                                Sum, Closure Members                                                                         131    102    1    3    3    96                                Sum, All leaks 343    307    12   11   67   378                               Percent of Containers                                                                        100    100    12   11   60   100                               of Set Leaking                                                                ______________________________________                                    

Sets B and C from Table 1 particularly suggest that the reclosableplastic containers employing layered sidewalls which curl toward oneanother in the process of being free-edge sealed (as in Set C) aresubstantially less likely to leak along the wire seals thereof, thancontainers conventionally made from the same materials in asubstantially homogeneous blend (Set B).

It should be noted that the success of the present invention is notdependent on, nor does the present invention necessarily adverselyaffect, the room temperature curling properties and machinability ofthose layered film portions of which the free edge-sealed articles ofthe present invention are to be comprised. In fact, some films having alesser tendency to curl at room temperature have been found to curl to agreater extent in a free edge-sealing process, and to form better sealswhen stacked and arranged in accordance with the present invention, thanother films which curl to a larger extent at room temperature.

While preferred embodiments of the free edge-sealed articles of thepresent invention and of a method for making such articles have beendescribed and exemplified herein, it will be appreciated that numerouschanges can be made thereto without departing in scope or spirit fromthe invention disclosed herein and defined by the appended claims.

What is claimed is:
 1. A free edge-sealed film article comprising twofilm portions and containing a free edge-seal between said filmportions, wherein at least one of said free edge-sealed film portionsconsists essentially of a plurality of layers of diverse thermoplasticmaterials, said plurality of layers being ordered so that on sealingsaid film portions together, said layered film portion curls toward theother of said two film portions along at least a portion of thefree-edge seal.
 2. A free edge-sealed film article as defined in claim1, wherein the diverse thermoplastic materials are characterized bydiffering amounts of frozen-in stress.
 3. A free edge-sealed filmarticle as defined in claim 1, wherein the at least one free edge-sealedfilm portion consists essentially of two layers of two diversethermoplastic materials.
 4. A free edge-sealed film article as definedin claim 3, wherein the two free edge-sealed film portions aresubstantially identically constructed.
 5. A free edge-sealed filmarticle as defined in claim 4, wherein each of the two free edge-sealedlayered film portions is less than about 2.0 mils in thickness.
 6. Afree edge-sealed film article as defined in claim 4, wherein the twofree edge-sealed layered film portions each consist essentially of onelow density polyethylene layer and one linear low density polyethylenelayer.
 7. A free edge-sealed film article as defined in claim 6, whereinthe two free edge-sealed layered film portions are formed bycoextrusion.
 8. A free edge-sealed film article as defined in claim 6,wherein the linear low density polyethylene layer in each of the twofree edge-sealed layered film portions has a density of from about 0.912to about 0.941 grams per cubic centimeter.
 9. A free edge-sealed filmarticle as defined in claim 8, wherein the linear low densitypolyethylene layer comprises, in each of the two free edge-sealedlayered film portions, from about 30 to about 70 percent of thethickness on average of the at least two free edge-sealed layered filmportions.
 10. A free edge-sealed film article as defined in claim 1,wherein the article is a reclosable plastic container of the typecomprising two flexible opposed free edge-sealed sidewalls and aninterlocking closure mechanism operable for being interlocked over apredetermined length and connected to the sidewalls adjacent, an openend of the container.
 11. A free edge-sealed film article as defined inclaim 10, wherein the interlocking closure mechanism comprises a pair ofopposed interlocking closure members, each opposed interlocking closuremember extending substantially continuously over the predeterminedlength for interlocking with the other of the pair of closure membersover the predetermined length.
 12. A free edge-sealed film article asdefined in claim 11, wherein on sealing said two sidewalls together eachof said sidewalls is curled toward the other of said sidewalls along theentirety of each of said at least two edges.
 13. A free edge-sealed filmarticle as defined in claim 11, wherein the diverse thermoplasticmaterials are characterized by differing amounts of frozen-in stress.14. A free edge-sealed film article as defined in claim 13, wherein thetwo flexible opposed free edge-sealed sidewalls each consistingessentially of two layers of two diverse thermoplastic materials.
 15. Afree edge-sealed film article as defined in claim 14, wherein thesidewalls are substantially identically constructed.
 16. A freeedge-sealed film article as defined in claim 14, wherein each of the twofree edge-sealed sidewalls is less than about 2.0 mils in thickness. 17.A free edge-sealed film article as defined in claim 15, wherein the twofree edge-sealed sidewalls each consist essentially of one low densitypolyethylene layer and one linear low density polyethylene layer whichhave been coextruded together.
 18. A free edge-sealed film article asdefined in claim 17, wherein the linear low density polyethylene layerin each of the two free edge-sealed sidewalls has a density of fromabout 0.917 to about 0.935 grams per cubic centimeter.
 19. A freeedge-sealed film article as defined in claim 18, wherein the linear lowdensity polyethylene layer comprises, in each of the two freeedge-sealed sidewalls, from about 35 to about 65 percent of thethickness on average of the sidewalls.
 20. A free edge-sealed filmarticle as defined in claim 19, wherein the linear low densitypolyethylene layer comprises, in each of the two free edge-sealedsidewalls, from about 45 to about 55 percent of the thickness on averageof the sidewalls.
 21. A free edge-sealed film article as defined inclaim 12, wherein the article comprising layered, flexible opposed freeedge-sealed sidewalls demonstrates less than about 20 percent as manyleaks when blown up in the manner of a balloon and submersed underwaterthan an article which is otherwise substantially identicallyconstructed, blown up and submersed, but which comprises flexibleopposed free edge-sealed sidewalls consisting essentially of the samediverse thermoplastic materials in a substantially homogeneous blend.22. A free edge-sealed film article as defined in claim 21, wherein thearticle comprising layered, flexible opposed free edge-sealed sidewallsdemonstrates less than about 10 percent as many leaks when blown up inthe manner of a balloon and submersed underwater than an article whichis otherwise substantially identically constructed, blown up andsubmersed, but which comprises flexible opposed free edge-sealedsidewalls consisting essentially of the same diverse thermoplasticmaterials in a substantially homogeneous blend.